Amazon has launched a pharmacy business, offering to fill prescriptions for delivery by mail.

The retail giant barging in — its biggest foray into health care yet — reverberated through the industry on Tuesday. Shares of CVS were down about 8% at midday, while Walgreens tumbled 9% and Rite Aid 15%.

Prescription drugs are an industry worth hundreds of billions of dollars — and more people have turned to ordering medications by mail during the coronavirus pandemic.